1. Field of the Invention
The present invention relates to a brake system for a vehicle, and more particularly, to a brake system for a vehicle, which can supplement brake negative pressure without increasing the capacity of a vacuum pump.
2. Description of Related Art
In general, as a vehicle becomes large-sized and has high speed, a brake booster is used in a brake pedal in order to ensure a braking force of the vehicle. The brake booster has a power piston that is installed separately from a mast cylinder, and high pressure is generated by applying a differential pressure between vacuum and atmospheric pressure to the power piston or by increasing the force applied thereto.
Such a brake booster may be classified into a vacuum brake booster that uses a differential pressure between vacuum and atmospheric pressure and a compressed air brake booster that uses compressed air pressure. The vacuum brake booster is a device that applies large force to the brake by applying a differential force between negative pressure that is generated from an intake manifold of an engine or a vacuum pump and atmospheric pressure to the booster.
In the case of using such a vacuum pump, negative pressure that is generated from the intake manifold of the engine is typically used. FIG. 3 is a schematic view illustrating a brake system in the related art. As illustrated in FIG. 3, according to a brake system 200 in the related art, in order to generate negative pressure, a VIS (variable induction system) actuator 210 of an intake manifold is connected to a VIS vacuum pipe 230 through a VIS valve 220. The VIS vacuum pipe 230 is connected to a vacuum pump 250 through a brake nipple 240. The vacuum pump 250 generates and applies necessary negative pressure to a brake booster.
In the brake system 200 in the related art, however, the whole negative pressure that is required in the engine is generated by the vacuum pump, and if the negative pressure is insufficient, it is necessary to increase the capacity of the vacuum pump 250. In the case of increasing the capacity of the vacuum pump 250, frictional force is increased depending on the increase of a driving force of the vacuum pump 250, and thus load sharing occurs for the driving force of the weighted vacuum pump 250 to deteriorate the fuel efficiency and engine output torque. Further, in the case of using the negative pressure that is generated in the intake manifold of the engine, the generated negative pressure is not uniform, but varies depending on the surrounding environment, such as low air density in the high elevated areas, resulting in that it is difficult to ensure uniform negative pressure that is necessary for the booster.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.